<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Vue 数据</title>
    <script src="../vue.js"></script>
</head>
<body>
    <div id="app">
        
        <input type="text" v-model="cityName">
        <p>{{message | toUpcase}}</p>
        <div v-bind:id="dataId | formatId">helloworld</div>
    </div>
    <script>
        var vm=new Vue({
            el:'#app',
            data:{
              cityName:'shanghai',
              message:'helloworld',
              cityId:'dff1',
            },
            watch:{
                cityName (newName, oldName){
                    console.log(newName, oldName)
                }
            },
            filters:{
               toUpcase (value){
                   return value ? value.toUpCase():''
               },
            
               formatId(value){
                   return value ? value.charAt(1)+value.indexOf('d'):''
               }
            }

        })
    </script>

</body>
</html>